I would just replace it. A replacement yoke like that is not terribly expensive and you will probably spend as much or more repairing it.
If the yoke has great sentimental value, you can probably repair it by filling in the crack and missing wood (along with the original screw holes) with epoxy, but I would then definitely glass over the area of repair on both sides. Then just drill new holes for the machine screws.
The glass will be transparent when wetted out and the weave filled with epoxy but the glassed area will be a slightly different color after you oil or varnish the thwart.
The ends of thwarts often rot because any water in the boat runs along under the inwales when the boat is inverted. The moisture saturates the end of the thwarts and the screw holes that the machine screws go through and rots the wood over time.
I agree that it is important to try to seal the cut ends of the thwarts somehow. I also like to drill the holes for the machine screws slightly bigger than needed so I can seal the wood exposed by the hole.
I have just used either varnish or penetrating oil, but Doug's idea of using epoxy is probably even better.
EZ-Dock modular docks
Bent Shaft Canoe Paddles
Kayak Deck Gear Bags
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